Micronutrients are those nutrients which are essential for plant growth but which are required in amounts which are typically less than that required for macronutrients such nitrogen, phosphorus and potassium. The seven micronutrients commonly understood to be necessary for plant growth are boron, chlorine, copper, iron, manganese, molybdenum and zinc. Cobalt, calcium, magnesium and sulfur may also be required in smaller amounts, and are variously classified as micronutrients or secondary nutrients. As used herein, the term micronutrients includes secondary nutrients.
The constituent elements of micronutrients must be presented to plants in a form suitable for plant uptake, translocation and assimilation. One way in which certain micronutrient metals have been successfully applied to and utilized by plants is by application of metal chelate solutions. The term chelate is from the Greek for claw, and describes a "complex" in which organic molecules form ring-like structures through coordinate bonds with metal ions. The metal chelate structure loosely ties up the constituent metal ion(s) in a form in which the metal component is less likely to dissociate or participate in chemical reactions when the chelate is in the soil or in solution with other fertilizers. This allows the chelated metal to remain available until after the product penetrates and translocates within plant.
Chelated metals are currently available in the fertilizer industry in powder and liquid forms. Each form has certain disadvantages, however, and both forms tend to be more expensive than inorganic metal compounds. For example, aqueous metal chelate formulations typically are supplied in 2.5 or five gallon plastic jugs containing from 5% to 9% by weight of the chelated metal. Cost of shipping these products is high, primarily because of the relatively low weight percent of the chelated metal in the product as compared to the volume of water in which the metal chelate is dissolved. In addition, if temperatures drop below 32.degree. F. some metal chelates crystallize out of liquid formulations and concentrate at the bottom of the container. Naturally this creates problems when subsequently applying the metal chelate solution to crops.
Not only does the bulkiness of the containers pose a storage space problem for some growers or fertilizer dealers, disposal of the plastic jugs can be problematical because many landfills no longer accept these containers because of container bulkiness and contamination issues. To address problems associated with use of plastic jugs, growers crops for which metal chelate requirements are substantial may choose to buy aqueous metal chelates solutions in bulk and place the liquids in large tanks or other storage vessels. However, to avoid accidental spillage when using such storage vessels, individual storage vessels are preferably placed in a lined dike having a capacity 110% of the volume of the largest storage vessel. This technique involves substantial cost to the grower or fertilizer dealer, and does not obviate crystallization problems of metal chelate solutions at lower temperatures.
While powder metal chelates are available and solve some of the stability, storage and disposal problems associated with metal chelate solutions, other problems remain unaddressed. For example, to produce certain powdered metal chelates, constituents are reacted in an aqueous solution and then dried, a process requiring substantial time, energy and expense. Powdered metal chelates produced in this manner include ethylene diamine tetraacetic acid (EDTA) chelates and lignin sulfonate- based metal chelates. While these powdered metal chelates can provide the constituent metal in greater concentration than metal chelate solutions, (e.g., 6% to 15% weight percent), powdered metal chelates are substantially more expensive, e.g., $1.50 to $8.00 per pound. The high cost of these products tends to limit their use to the horticulture industry.
Furthermore, some metal chelates solutions are decomposed by acid. The constituent metals may then exhibit reduced agronomic effectiveness. Thus, mixing some metal chelate solutions, including reconstituted powdered metal chelates, with certain acidic fertilizers must be avoided prior to application of the metal chelate solution to plants. Yet application of micronutrients with macronutrient fertilizers is typically preferred, because it provides a way to more evenly distribute a small micronutrient volume over a large target acreage.
It is against this background that the significant improvements and advancements of the present invention have taken place.